From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: Re: [Patch net] af_unix: revert "af_unix: use freezable blocking calls in read" Date: Thu, 17 Nov 2016 14:47:10 -0800 Message-ID: References: <1479420564-15799-1-git-send-email-xiyou.wangcong@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: netdev , Dmitry Vyukov , Tejun Heo , "Rafael J. Wysocki" To: Colin Cross Return-path: Received: from mail-yb0-f196.google.com ([209.85.213.196]:35417 "EHLO mail-yb0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750849AbcKQWrb (ORCPT ); Thu, 17 Nov 2016 17:47:31 -0500 Received: by mail-yb0-f196.google.com with SMTP id d59so9070840ybi.2 for ; Thu, 17 Nov 2016 14:47:31 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Nov 17, 2016 at 2:30 PM, Colin Cross wrote: > On Thu, Nov 17, 2016 at 2:09 PM, Cong Wang wrote: >> Commit 2b15af6f95 ("af_unix: use freezable blocking calls in read") >> converts schedule_timeout() to its freezable version, it was probably >> correct at that time, but later, commit 2b514574f7e8 >> ("net: af_unix: implement splice for stream af_unix sockets") breaks >> the strong requirement for a freezable sleep, according to >> commit 0f9548ca1091: >> >> We shouldn't try_to_freeze if locks are held. Holding a lock can cause a >> deadlock if the lock is later acquired in the suspend or hibernate path >> (e.g. by dpm). Holding a lock can also cause a deadlock in the case of >> cgroup_freezer if a lock is held inside a frozen cgroup that is later >> acquired by a process outside that group. >> >> The pipe_lock is still held at that point. So just revert commit 2b15af6f95. > > On my phone 77 threads are blocked in unix_stream_recvmsg. A simple > revert of this patch will cause every one of those threads to wake up > twice per suspend cycle, which can be multiple times a second. How > about adding a freezable flag to unix_stream_read_state so > unix_stream_recvmsg can stay freezable, and unix_stream_splice_read > can be unfreezable? Fair enough, I didn't know it could have such an impact. I will send v2. Thanks.